This is a proposal to study aspects of the biogenesis of messenger RNA (mRNA) in eukaryotes. Suspension cell cultures of human (HeLa) and mouse (myeloma) cancer cells are used to study the synthesis of heterogeneous nuclear RNA (hnRNA) and the mRNA derived from it by a series of processing enzymes. Short transcribed homopolymeric sequences designated as oligo A and oligo U have been found in hnRNA. Oligo U is also present in about 10 percent of the mRNA molecules. The detailed characterization of those mRNA's that contain oligo U can now be undertaken since a procedure has been devised recently for isolating oligo U containing mRNA that depends on the oligo U sequence. Studies of the translatability and turnover of oligo U (plus) mRNA and the localization of the oligo U sequence within mRNA are planned. Nuclei from mouse myeloma cells are being examined for their ability to initiate and process RNA made in vitro. Polyadenylation as a key step in processing nuclear transcripts will be examined in detail with these nuclei.